Preventing scalping of flavor or aroma components into the walls of plastic containers is a matter growing concern in the packaging industry. Flavor and aroma components, mostly volatile organics, are typically present at parts per million or even at parts per billion levels. Most common plastics, such as polyethylene, polypropylene, polystyrene, etc., tend to absorb, entirely or selectively, such volatile organics thereby either distorting or depriving the product of its intended taste and aroma.
One method of solving this problem has been by modifying the surface of polyethylene using fluorination. A number of flavor-sensitive products, however, such as juices, are "hot-filled" or filled at temperatures far above the softening and distortion points for polyethylene, thereby making such containers unsuitable for these uses.
Using polypropylene for such containers is an attractive alternative from cost, strength, and temperature resistance standpoints; however, like polyethylene, polypropylene also vigorously scalps flavor and aroma components from packaged goods, especially food products. Fluorinating polypropylene containers has proven to be significantly less successful in preventing the scalping of flavor/aroma components, therefore also making such containers undesirable for many applications.
Joffre, U.S. Pat. No. 2,811,468 teaches a method of imparting barrier properties to polyethylene films by fluorinating at least one surface of said film to contain not more than about 3.5% by weight fluorine, and enough fluorine such that the surface shows reduced permeability to the passage of atmospheric gases there through.
Dixon, et al. U.S. Pat. No. 3,862,284 teaches a process for improving the barrier properties of thermoplastic hollow blow-molded articles, by mixing into the blowing gas about 0.1% to 10% by volume fluorine, with the balance of the blowing gas typically being inerts. Additionally, it is also disclosed that the addition of a variety of other reactive gases such as sulfur dioxide, carbon monoxide, carbon dioxide, oxygen, chlorine, bromine, etc. can also enhance the physical properties of the container.
Beck, U.S. Pat. No. 4,550,043 discloses preforms for use in blow molding containers which are suitable for use in conjunction with hot products which must be subjected to pasteurization. The preform comprises inner and outer first layers of a thermoplastic resin, inner and outer layers of a barrier material next to and between said inner and outer first layers and a second layer of thermoplastic resin between said barrier material layers; wherein said second layer of thermoplastic material has a high thermal stability.